Figure 3
Large-range tuning of the twist angle to find the critical angle for resonant Raman. (a) The first Brillouin zone (BZ) of twisted bilayer graphene misoriented by θ. (b) Electronic bands in the vicinities of two Dirac cones. Van Hove singularities (vHs) are induced by band overlap. (c) Energy difference of the two vHs versus the twist angle θ. The gray dashed line indicates the excitation laser energy EL = 1.96 eV in our Raman measurement, corresponding to a twist angle of ~ 10°. (d) Raman spectra of a twistable bilayer graphene devices at a few representative twist angles. At θ = 10°, the graphene G-peak is largely enhanced. (e) The normalized graphene G-peak intensity as a function of the twist angle θ. Large enhancement at θ = 10° corresponds to the predicted resonant Raman.
